Photovoltaic modules, devices, or cells, can include multiple layers (or coatings) created on a substrate (or superstrate). For example, a photovoltaic device can include a barrier layer, a transparent conductive oxide layer, a buffer layer, and a semiconductor layer formed in a stack on a substrate. Each layer may in turn include more than one layer or film. For example, a semiconductor window layer and a semiconductor absorber layer together can be considered a semiconductor layer. Additionally, each layer can cover all or a portion of the device and/or all or a portion of a layer or a substrate underlying the layer. For example, a “layer” can include any amount of any material that contacts all or a portion of a surface. Cadmium telluride has been used for the semiconductor layer because of its optimal band structure and a low cost of manufacturing.
In order to electrically connect the photovoltaic device, a back contact layer can also be used. The back contact layer can include an electrically conductive material deposited onto the semiconductor layer. The back contact material is typically a metal selected for sufficient adhesion to the semiconductor window layer and minimal formation of a back contact barrier that can affect the current-voltage characteristics of the photovoltaic device. The back contact material is critical to photovoltaic device performance.
A known back contact material for photovoltaic devices includes polycrystalline zinc telluride. A formation of the polycrystalline zinc telluride has been performed by sputter deposition of zinc and telluride targets in a furnace at high temperatures, for example, above 280° C. The process of forming polycrystalline zinc telluride at high temperatures in a furnace is undesirably expensive, and increases a complexity in manufacturing the photovoltaic device. Other means for forming the polycrystalline zinc telluride have included epitaxial growth at lower temperatures by molecular beam epitaxy, another process which is also expensive and time consuming.
There is a continuing need for a low cost method for producing large area back contact layers of polycrystalline zinc telluride for photovoltaic modules. Desirably, the method is conducted at ambient temperature and minimizes a complexity in manufacturing photovoltaic modules.